Rotary drum filters are well known and are used in the pulp and paper industry to filter and wash pulp slurries. These filters generally comprise a cylindrical drum mounted for rotation in a tank containing a slurry solution. A filter deck assembly is mounted radially outward of the surface of the drum. As the drum is rotated, a low pressure is maintained inside the drum so that a pulp sheet is formed on the surface of the filter deck. The deck assembly functions to space the pulp from the drum surface to facilitate filtering and drainage. The deck assembly usually includes a drainage deck to direct the filtrate to filtrate compartments. The liquid filtrate is drawn through the filter deck and the drainage deck and into the filtrate compartments by a pressure differential. Filtrate is removed from the filtrate compartments in a conventional manner.
The deck assembly must prevent rewetting of the pulp sheet as the drum rotates through the descending path of the filtrate cycle.
Metal plates having fine perforations are often used as the filter deck. Corrugated sheets attached underneath the filter decks are used as the drainage deck. The metal plates, the corrugated sheets, and the drum may each be made of different metals. The deck assembly of rotary drum filters must be capable of withstanding differential thermal expansion of the component elements due to the temperature variations in presently known filtering cycles. For example, temperature differentials of up to 100.degree. F. expose the deck assembly to heavy thermal shocks once every cylinder revolution.
An object of the present invention is to provide a deck assembly for a rotary drum filter which is constructed and arranged to permit thermal expansion of the component elements without resultant damage.
It is another object of the present invention to provide a deck assembly which effectively prevents rewetting of the pulp sheet from a run back of the filtrate as the drum rotates through the descending path of the cycle.
It is another object of the present invention to provide a deck assembly which is particularly constructed and arranged to allow ready and simple replacement of deck sections.
It is another object of the present invention to provide a deck assembly which is constructed and arranged to be durable.
In general, the foregoing objects are obtained in a rotary drum filter having a plurality of longitudinally extending division grids mounted about the other circumference of a drum. A plurality of corrugated sheets are provided, with the leading and trailing edges of each sheet mounted to circumferentially adjacent pairs of division grids to define filtrate compartments. An equivalent number of perforated filter plates are also provided. Each filter plate is attached to the top of a corrugated sheet and has a leading edge that is set back from the leading edge of the attached sheet. A seal member is positioned at the leading edge of each corrugated sheet and has a first leg extending between the filter plate and the corrugated sheet. The seal member further includes a second leg which abuts the leading edge of the corrugated sheet so as to seal the open ends at the leading edge of the corrugated sheets.